My cold idle has always been a little off, but it got unbearable after I installed a lightened M20 flywheel and a 93 Octane Mark D chip. The car was much quicker, but when the engine was cold (in summer) it would die within a few seconds of starting. To keep it from dying I had to give it gas for about a half-minute. Then it would idle fine for a few seconds before the revs would gradually drop until the engine almost died and the idle control valve (ICV) would kick in and raise them back to normal. This oscillation would continue until the engine would warm up and then it idled fine.
On inspection I saw that most of my vacuum tubes that live under the intake manifold were cracked. From researching online I also found that a worn out ICV is often the culprit of an unstable idle. I figured the best bet was to replace both the hoses and the ICV since the replacement of both requires the effort of removing the intake manifold.
If your vacuum tubes haven't been replaced, you should definitely inspect them because they dry rot regardless of the number of miles on your car. You can try taping them, but without removing the manifold you can't access most of them, and if you do that, you might as well just replace them.
I think its possible to rebuild your ICV, but for the price I felt it was worth (and more expedient) to go with a new one.
Using RealOem I came up with the following parts list:
(1) 11151739266 Breather Hose
(1) 11151277301 Connector
(1) 13541739248 Hose
(1) 13411721907 Idle speed ctl. hose
(1) 13411721909 Hose
(1) 13411721972 Idle speed ctl. hose
(1) 13411721971 Idle speed ctl. hose
(2) 11151727393 Connector
(1) 11611717761 Intake manifold gasket
for a total of $76.37 from Crevier and
(1) 13411433627 Idle Control Valve
for a total of 137.86 from BMA (about $40 cheaper)
I reused the old hose clamps, so they are not on the list.
I would also add (1) 11151717858 vent hose which I missed and was cracked but I taped and reused.
Disclaimer: I didn't consult a manual so
follow these instructions at your own risk.
This job took me about 2-3 hours (could probably be done faster if you know what you are doing :rolleyes:) and I did it in my car-port with just basic sockets, extenders, screwdrivers, and wrenches.
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Study this diagram:
http://www.m42club.com/forums/attachment.php?attachmentid=381&d=11560435631. Start by removing the boot that goes from the intake box to the throttle body as well as the hose that attaches from the boot to the vacuum lines.
2. Remove the horseshoe plate on the front underside of the throttle body (TB) so you can access the studs behind it. Also remove the wiring harness that attaches to TB.
3. Remove the four bolts that attach the throttle body to the manifold via studs, take care not to drop any of the bolts (like I did), they're a bitch to recover once you do.
4. As you remove the TB, remove the three hoses that attach to it and note their locations. Lay the TB to the side on the strut tower, you don't have to remove the throttle cable.
5. Remove the 8 bolts that hold the intake manifold from the front and the 2 that hold it from the sides (at the plenum)
6. Carefully pull the manifold up off the studs. You'll have to wrangle with the TB heater plates to get them to slide through the opening, or you could remove them completely. I removed the coolant hose from the right side of the lower plate to make it easier.
7. With the manifold removed you have easier access to the hoses underneath. Start removing the cracked hoses, noting their locations and order. To remove you two center hoses that have the U shaped pipe running through them, you will need to remove the 2 coolant hoses that attach to the ends of the U pipe by loosening their hose clamps.
8. With the U pipe removed, note the location and orientation of the two hoses that are slid over it, then remove and replace them with the respective hoses one-by-one. I used a little soapy water to make them slide on easier. On the right side of the U pipe I attached the coolant hose that I removed the the right side of the lower TB heater plate. On the left hose (the end that extends forward) I attached the angle connector and short hose that attaches to the bottom of the TB.
9. Noting its location and orientation, remove the old ICV and switch the mount over to your new one. Attach the top hose that goes the the plenum.
10. At this point you can replace all the old hoses and try to get everything back in the way it was before it came out. The trickiest bit for me was connecting the hose that goes from the right side of the right U hose to the ICV. My approach was to slide the hose into position under the lower manifold then attach it to right U hose. Once you get that in place the rest of it is fairly easy to reattach. Make sure to get everything in place remember to tighten everything before you start putting manifold back on.
11. Re-installation is reverse of removal with the addition of replacing the manifold gasket for good measure. I couldn't find torque specs on the manifold studs, but I don't think they need to be terribly tight. Find torque specs if you can.
12. After getting it all back together, you will need to bleed your coolant system since you opened it up. Start your engine and let it warm up. When the upper hose is warm you can start bleeding it. Have someone rev your engine to 2500-3000 rpms while you open the bleed valve on your radiator. You should see some air come out. Leave it open until only coolant and no air is coming out. Clean up and your done!
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Hopefully when you started it up, if everything went well, it started in on a nice smooth steady idle like mine did. After driving it around a bit, I think mine has even gotten better.
I know there are lots of idle issues out there, and this procedure might not cure all of them, but I think its a good place to start.
Topic: Improve your cold idle by replacing cracked vacuum tubes and ICV (Read 9618 times)